The present invention relates to a method for guiding an acoustic torpedo toward a ship which has been selected as a target and which is dragging one or more noise generating decoys, i.e. so-called disturbance generators, as a defense against torpedoes, and to an apparatus for implementing this method.
It is known to use acoustic torpedoes for the automatic search and attack of ships. Such acoustic torpedoes are equipped with a sound-detecting system which is highly sensitive in the forward direction. This sound-detecting system is able to detect the sound radiation of a moving ship and utilize it to guide the torpedo.
To defend the ship against automatically guided acoustic torpedoes it is known to frequently change course and to use noise generating decoys or disturbance generators. These disturbance generators are dragged behind the ship, with the length of the drag line and the moment of use of the disturbance generators being variable. The disturbance generators are provided with guide surfaces or the like so that they can be used with different drag angles and so that they may also be outside of the actual path of the ship. The disturbance generators produce a noise which has a much greater volume than the moving ship. Consequently the torpedo is caused to approach and attack the disturbance generator rather than the ship since the sound detection system of the torpedo always directs the torpedo toward the strongest or loudest noise source.
Several methods are known which overcome this drawback and which make it possible, even in the presence of a strong noise source, to detect further noise sources. For example, Federal Republic of Germany Offenlegungsschrift (Laid-open Application No. 2,059,155, published Oct. 7, 1971) discloses a method which detects a plurality of noise sources on the basis of significantly different frequencies and permits the indication of the direction of the noise sources by means of frequency selection. However, this method requires that every noise source have its own specific frequency.
This last requirement is not necessary with the method disclosed in Federal of Germany Offenlegungsschrift No. 2,417,0800, published Oct. 9, 1975. With that latter method, it is possible to determine and indicate the direction of a plurality of noise sources even if these noise sources have the same frequency spectra. The individual noise sources are determined with the aid of a gradient ranging system in order to form and pivot cardioid characteristics. However, such a process is rather complicated and time consuming since every noise source must have its own cardioid characteristic and the individual cardioid characteristics must be aligned one after the other with the individual noise sources. Such a method cannot be used to determine a disturbance generator during a torpedo attack since an attacked ship is able to defend itself with a plurality of disturbance generators which would all have to be detected one after the other.
A further method for differentiating between a plurality of noise sources is disclosed in Federal Republic of Germany Offenlegungsschrift No. 2,525,569, published Dec. 21, 1978. This method utilizes the differences between the sound spectrum of a disturbance generator and that of a ship and the fact that a ship gives off stochastic or random noise components in addition to periodic noise components, while a disturbance generator emits only periodic noise. A correlative testing method is used to evaluate the different noises.
Some of the above-mentioned methods are rather complicated and some require certain conditions in order to operate properly.